Conventional pumping machines that can be used for difficult-to-pump materials have displacement organs such as pistons, plungers, peristaltic hoses etc. However such displacement organs are subject to frictional wear and the drive of the machine is not properly isolated from the pumped material.
U.S. Pat. No. 8,096,785 discloses a hydraulically driven multicylinder diaphragm pumping machine, in particular for pumping difficult-to-pump materials. This pumping machine comprises a plurality of pump cylinders each having one end with an inlet and outlet for fluid to be pumped and another end with an inlet and outlet for hydraulic fluid. These inlets and outlets can be a separate inlet and outlet (for the hydraulic fluid) or a combined inlet/outlet (for the fluid material being pumped). The inlets and outlets are associated with respective inlet and outlet valves.
In such machines, a separator is located inside and is movable to-and-fro along each pump cylinder. The movable separator has one side facing the pumped-material end of the cylinder and another side facing the hydraulic-fluid end of the cylinder. This movable separator is connected to the inside of the pumped-material end of the cylinder by a first flexible diaphragm in the form of a concertina-like bellows that is expandable and contractable inside the cylinder along the length direction of the cylinder as the movable separator moves to-and-fro along the cylinder. The movable separator delimits a first chamber inside the first bellows-like flexible diaphragm for containing a variable volume of pumped fluid in communication via the inlet and outlet with a pumped fluid manifold and circuit. The movable separator is connected also to the inside of the second end of the cylinder by a second flexible diaphragm in the form of a concertina-like bellows that is contractable and expandable along the length direction of the cylinder in correspondence with expansion and contraction of the first flexible diaphragm. The second side of the movable separator delimits a second chamber inside the second expandable and contractable diaphragm for containing a variable volume of hydraulic fluid in communication with the second inlet and outlet. An annular space is defined between the outside of the first and second diaphragms and the inner wall of the pump cylinder which annular space in use contains a fluid that is the same as said hydraulic fluid or has similar hydraulic characteristics.
This double bellows pumping machine is directly driven by a hydraulic pump drive, greatly simplifying the machine and providing simple means of variation and control of the flow of the pumped fluid delivered. Moreover, the double diaphragm arrangement provides a double protection of the pumped fluid from the pumping fluid.
Supplemental research with such machines demonstrated that various aspects such as the reliability of the operation of the bellows-like diaphragm could be improved, which led to the improved double-bellows pump described in U.S. Pat. No. 8,591,201.
Experience with these two-bellows pumps has shown that they provide excellent pumping characteristics notably a smooth pumping action; however in case of puncture of a bellows its replacement requires a substantial overhaul of the machine that can take a day or more.
Furthermore, conventional positive displacement pumps designed for use in oilfields and off-shore platforms have numerous drawbacks. First, they have many mechanical moving parts, causing wear and tear, heat and friction. Moreover, most conventional pumps are too large to be easily transported on a truck and are not built to work under classified conditions. Conventional pumps also result in vibrational premature valve wear and packing/sealing problems. Most pumps are too heavy to transport around the oilfields and off-shore platforms. Conventional pumps operate at over 300 strokes per minute, leading to increased friction, heat and wear. Conventional pumps operate at high decibel levels, which is a major issue when working around people. No known positive
displacement pump can pump a wide variety of liquids without frequent changes of pistons, sleeves and other components.
It follows that there is room for improvement of conventional positive displacement pumps.
EP-0 419 695 A1 discloses a slurry pumping apparatus comprising two side-by-side diaphragm-type pumping units. Each pumping unit comprises a hydraulic cylinder integral with and superimposed on a diaphragm-type pumping cylinder. The hydraulic cylinders each have a double piston arrangement and are connected between the pistons to alternately and repetitively deliver slurry from a slurry tank into processing equipment via the pumping cylinders.